The invention described herein was made in the course of, or under, Energy Research and Development Administration Contract No. W-7405-ENG-48 with University of California.
This invention relates to a method of separating isotopes, particularly of carbon or nitrogen, by selective photodissociation, that is, selective photoexcitation followed by chemical dissociation. More particularly, this invention relates to the enrichment of carbon and/or nitrogen isotopes by selective photodissociation of an azo compound or a diazoalkane.
.sup.15 N and .sup.13 C occur naturally with an abundance of 0.37% and 1.11%, respectively, and the present cost of each isotope is about $1000/mole for 95% enriched substance. .sup.15 N is useful as a radioactive tracer to study the movement of fertilizers, nutrients and pollutants in the biosphere and is also useful in the form uranium nitrate in fission reactors; both .sup.13 C and .sup.15 N are useful as medical and geophysical tracers. The present cost of these isotopes make them attractive candidates for a low cost laser isotope separation process.
Laser isotope separation processes involve (1) selective photoexcitation, which makes use of the phenomenon known as isotope shift, i.e., a slight shift of the lines in the absorption spectra of elements or molecules due to the small difference in nuclear mass of the isotopes of the same element contained therein, and (2) a mechanism for separating selectively excited species from nonexcited species.
In selective photodissociation, separation is achieved by dissociation of the excited species without substantial dissociation of nonexcited species. In general, the dissociation products are smaller molecules of greatly enriched isotope content which are easily separated from the reaction mixture by standard chemical means. Dissociation of the excited species may occur spontaneously or may require the absorption of additional photons (multiphoton absorption process). A general description of selective photodissociation schemes is given in C. B. Moore, Accounts of Chemical Research 6 323 (1973).